102. 二叉树的层序遍历

Introduction

Question：102. 二叉树的层序遍历

Analysis

比较简单，直接用队列做广度优先遍历就好了。

Implement

vector<vector<int>> levelOrder(TreeNode* root) {
    vector<vector<int>> res;
    if (root==nullptr) return res;
    queue<TreeNode *> q;
    q.push(root);
    while(!q.empty()) {
        vector<int> vec;
        for(int i = 0, size = q.size(); i < size; i++) {
            root = q.front(); q.pop();
            vec.push_back(root->val);
            if (root->left) q.push(root->left);
            if (root->right) q.push(root->right);
        }
        res.push_back(vec);
    }
    return res;
}